linux-kernel - [PATCH 2/8] serial: tegra: Add delay after enabling FIFO mode

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Date:	Tue, 5 May 2015 15:17:53 +0100
From:	Jon Hunter <jonathanh@...dia.com>
To:	Laxman Dewangan <ldewangan@...dia.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>
CC:	<linux-serial@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Jon Hunter <jonathanh@...dia.com>
Subject: [PATCH 2/8] serial: tegra: Add delay after enabling FIFO mode

For all tegra devices (up to t210), there is a hardware issue that
requires software to wait for 3 UART clock periods after enabling
the TX fifo, otherwise data could be lost.

Signed-off-by: Jon Hunter <jonathanh@...dia.com>
---
 drivers/tty/serial/serial-tegra.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/tty/serial/serial-tegra.c b/drivers/tty/serial/serial-tegra.c
index 9e08d3f07509..0d9d7ceb1dbb 100644
--- a/drivers/tty/serial/serial-tegra.c
+++ b/drivers/tty/serial/serial-tegra.c
@@ -885,6 +885,16 @@ static int tegra_uart_hw_init(struct tegra_uart_port *tup)
 	tup->fcr_shadow |= TEGRA_UART_TX_TRIG_16B;
 	tegra_uart_write(tup, tup->fcr_shadow, UART_FCR);
 
+	/* Dummy read to ensure the write is posted */
+	tegra_uart_read(tup, UART_SCR);
+
+	/*
+	 * For all tegra devices (up to t210), there is a hardware issue that
+	 * requires software to wait for 3 UART clock periods after enabling
+	 * the TX fifo, otherwise data could be lost.
+	 */
+	tegra_uart_wait_cycle_time(tup, 3);
+
 	/*
 	 * Initialize the UART with default configuration
 	 * (115200, N, 8, 1) so that the receive DMA buffer may be
-- 
1.9.1

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